Hydraulic dashpots are employed to absorb the shock that accompanies the motion of spring-articulated wheel suspensions, preferably in motor vehicles.
The shock is absorbed by forcing fluid out of one compartment and into another in a cylinder through preferably spring-loaded ports in a piston.
A known method of ensuring well defined shock absorption at low piston speeds is to provide bypasses hydraulically paralleling the ports, the two compartments communicating through the bypasses. Providing the bypasses with variable open cross-sections is also known.
German 10 138 487 C1 discloses a dashpot of this genus. It includes a bypass accommodated in a bore through the center of the piston rod. The bypass operates in conjunction with lateral outlets leading out of the piston rod. The bypass is adjusted to the various motions of a dashpot piston in the device's cylinder (1) (compression phase and suction phase), by a control rod fitted with lateral flanges and traveling back and forth inside at least one tube. The tubes can be relatively adjusted axially and are provided with stops for the control rod flange.
There is a drawback to this system. Since the direction traveled by the control rod constantly changes in accordance with the direction traveled by the dashpot, and since the flanges are constantly hitting the stops, the control rod's mass is extremely heavy, and must be repeatedly accelerated. The control rate is accordingly limited in height, resulting in the creation of powerful forces and hence serious wear.